Carbon dioxide electrolytic device and method of electrolyzing carbon dioxide

ABSTRACT

A carbon dioxide electrolytic device comprises: an electrolysis cell including a cathode, an anode, a carbon dioxide source to supply carbon dioxide to the cathode, a solution source to supply an electrolytic solution, and a separator separating the anode and the cathode; a power controller connected to the anode and the cathode; a refresh material source including a gas source to supply a gaseous substance, and a solution source to supply a rinse solution; and a controller to control the carbon dioxide source, the solution source, the power controller, and the refresh material source in accordance with request criteria of a performance of the cell and thus stop the supply of the carbon dioxide and the electrolytic solution, and apply the voltage therebetween while supplying the rinse solution thereto.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2017-180389, filed on Sep. 20, 2017; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a carbon dioxideelectrolytic device and a method of electrolyzing carbon dioxide.

BACKGROUND

In recent years, depletion of fossil fuel such as petroleum or coal hasbeen concerned, and expectation for sustainably-usable renewable energyhas been rising. As the renewable energy, a solar cell, wind powergeneration, and the like can be cited. Because a power generation amountof these depends on weather and a natural situation, there is a problemthat it is difficult to realize stable supply of electric power. Forthis reason, there has been made an attempt to store the electric powergenerated by the renewable energy in a storage battery, to therebystabilize the electric power. However, when the electric power isstored, there are problems that a cost is required for the storagebattery, and a loss occurs at a time of the storage.

With respect to such points, attention is focused on a technology inwhich water electrolysis is performed by using the electric powergenerated by the renewable energy to produce hydrogen (H₂) from water,or carbon dioxide (CO₂) is electrochemically reduced to be convertedinto a chemical substance (chemical energy) such as a carbon compoundsuch as carbon monoxide (CO), formic acid (HCOOH), methanol (CH₃OH),methane (CH₄), acetic acid (CH₃COOH), ethanol (C₂H₅OH), ethane (C₂H₆),or ethylene (C₂H₄). When these chemical substances are stored in acylinder or a tank, there are advantageous points that a storage cost ofenergy can be reduced, and a storage loss is also small, when comparedto a case where the electric power (electric energy) is stored in thestorage battery.

As a carbon dioxide electrolytic device, for example, a structure inwhich an Ag nanoparticle catalyst is used as a cathode, a cathodesolution and CO₂ gas are brought into contact with the cathode, and ananode solution is brought into contact with an anode is being studied.As a concrete configuration of the electrolytic device, for example,there can be cited a configuration which includes a cathode solutionflow path disposed along one surface of the cathode, a CO₂ gas flow pathdisposed along the other surface of the cathode, an anode solution flowpath disposed along one surface of an anode, and a separator disposedbetween the cathode solution flow path and the anode solution flow path.When a reaction of producing, for example, CO from CO₂ is performed fora long period of time by using the electrolytic device having such aconfiguration and, for example, by making a constant current flowthrough the cathode and the anode, there is a problem that adeterioration over time of a cell performance such that a productionamount of CO is reduced or a cell voltage is increased occurs. For thisreason, there has been demanded a carbon dioxide electrolytic devicecapable of suppressing the deterioration over time of the cellperformance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a carbon dioxide electrolytic device of afirst embodiment.

FIG. 2 is a sectional view illustrating an electrolysis cell of thecarbon dioxide electrolytic device illustrated in FIG. 1.

FIG. 3 is a view illustrating one example of an anode solution flow pathin the electrolysis cell illustrated in FIG. 2.

FIG. 4 is a view illustrating one example of a cathode solution flowpath in the electrolysis cell illustrated in FIG. 2.

FIG. 5 is a view illustrating another example of the cathode solutionflow path in the electrolysis cell illustrated in FIG. 2.

FIG. 6 is a view illustrating one example of a CO₂ gas flow path in theelectrolysis cell illustrated in FIG. 2.

FIG. 7 is a view illustrating one example of a cathode in theelectrolysis cell illustrated in FIG. 2.

FIG. 8 is a view illustrating another example of the cathode in theelectrolysis cell illustrated in FIG. 2.

FIG. 9 is a view schematically illustrating a reaction in the cathode inthe electrolysis cell illustrated in FIG. 2.

FIG. 10 is a chart illustrating an operation step of the carbon dioxideelectrolytic device of the first embodiment.

FIG. 11 is a chart illustrating a refresh step of the carbon dioxideelectrolytic device of the first embodiment.

FIG. 12 is a view illustrating a carbon dioxide electrolytic device of asecond embodiment.

FIG. 13 is a sectional view illustrating an electrolysis cell of thecarbon dioxide electrolytic device illustrated in FIG. 12.

FIG. 14 is a view illustrating a carbon dioxide electrolytic device of athird embodiment.

FIG. 15 is a sectional view illustrating an electrolysis cell of thecarbon dioxide electrolytic device illustrated in FIG. 14.

DETAILED DESCRIPTION

A carbon dioxide electrolytic device, comprising: an electrolysis cellincluding a cathode to reduce carbon dioxide and thus produce a carboncompound, an anode to oxidize water or hydroxide ions and thus produceoxygen, a carbon dioxide source to supply carbon dioxide to the cathode,a solution source to supply an electrolytic solution containing water toat least one selected from the group consisting of the cathode and theanode, and a separator separating the anode and the cathode; a powercontroller connected to the anode and the cathode and configured toapply a voltage therebetween; a refresh material source including a gassource to supply a gaseous substance to at least one selected from thegroup consisting of the anode and the cathode, and a solution supplysource to supply a rinse solution to at least one selected from thegroup consisting of the anode and the cathode; and a controller tocontrol the carbon dioxide source, the solution source, the powercontroller, and the refresh material source in accordance with requestcriteria of a performance of the cell and thus stop the supply of thecarbon dioxide and the electrolytic solution, and apply the voltagetherebetween while supplying the rinse solution thereto.

Hereinafter, a carbon dioxide electrolytic device of an embodiment willbe described with reference to the drawings. In each embodimentpresented below, substantially the same components are denoted by thesame reference signs, and a description thereof is sometimes partiallyomitted. The drawings are schematic, and a relationship between athickness and a planar size, thickness proportions of the respectiveportions, and the like are sometimes different from actual ones.

First Embodiment

FIG. 1 is a view illustrating a configuration of a carbon dioxideelectrolytic device according to a first embodiment, and FIG. 2 is asectional view illustrating a configuration of an electrolysis cell inthe electrolytic device illustrated in FIG. 1. A carbon dioxideelectrolytic device 1 illustrated in FIG. 1 includes an electrolysiscell 2, an anode solution supply system 100 which supplies an anodesolution to the electrolysis cell 2, a cathode solution supply system200 which supplies a cathode solution to the electrolysis cell 2, a gassupply system 300 which supplies carbon dioxide (CO₂) gas to theelectrolysis cell 2, a product collection system 400 which collects aproduct produced by a reduction reaction in the electrolysis cell 2, acontrol system 500 which detects a type and a production amount of thecollected product, and performs control of the product and control of arefresh operation, a waste solution collection system 600 which collectsa waste solution of the cathode solution and the anode solution, and arefresh material source 700 which recovers an anode, a cathode, or thelike of the electrolysis cell 2.

As illustrated in FIG. 2, the electrolysis cell 2 includes an anode part10, a cathode part 20, and a separator 30. The anode part 10 includes ananode 11, an anode solution flow path 12, and an anode current collector13. The cathode part 20 includes a cathode solution flow path 21, acathode 22, a CO₂ gas flow path 23, and a cathode current collector 24.The separator 30 is disposed to separate the anode part 10 and thecathode part 20. The electrolysis cell 2 is sandwiched by a pair ofsupport plates, which are not illustrated, and further tightened bybolts or the like. In FIG. 1 and FIG. 2, there is provided a powercontroller 40 which makes a current flow through the anode 11 and thecathode 22. The power controller 40 is connected to the anode 11 and thecathode 22 via a current introduction member. The power controller 40 isnot limited to a normal system power supply, battery, or the like, andmay be one having a power source which supplies electric power generatedby renewable energy such as a solar cell or wind power generation. Notethat the power controller 40 may also have the aforementioned powersource and a power controller or the like that adjusts an output of theaforementioned power source to control a voltage between the anode 11and the cathode 22.

The anode 11 is an electrode (oxidation electrode) which causes anoxidation reaction of water (H₂O) in an anode solution as anelectrolytic solution to produce oxygen (O₂) or hydrogen ions (H⁺), orcauses an oxidation reaction of hydroxide ions (OH⁻) produced in thecathode part 20 to produce oxygen (O₂) or water (H₂O). The anode 11preferably has a first surface 11 a which is brought into contact withthe separator 30, and a second surface 11 b which faces the anodesolution flow path 12. The first surface 11 a of the anode 11 is broughtinto close contact with the separator 30. The anode solution flow path12 supplies the anode solution to the anode 11, and is formed of a pit(groove portion/concave portion) provided in a first flow path plate 14.The anode solution flows through inside the anode solution flow path 12so as to be brought into contact with the anode 11. The anode currentcollector 13 is electrically brought into contact with a surface on aside opposite to the anode 11 of the first flow path plate 14 whichforms the anode solution flow path 12.

As described above, in the electrolysis cell 2 of the embodiment, theanode 11 and the separator 30 are brought into close contact with eachother. In the anode 11, oxygen (O₂) is produced, and at this time, in acell structure in which a separator is sandwiched by a cathode solutionflow path and an anode solution flow path, air bubbles of oxygen (O₂)gas generated in the anode 11 stay in the anode solution flow path, anda cell resistance between the anode and the separator (ion exchangemembrane or the like) increases, this sometimes increases a voltagevariation of the anode. With respect to a point as above, the anodesolution flow path 12 is not disposed between the anode 11 and theseparator 30, and by making the anode 11 and the separator 30 to bebrought into close contact with each other, oxygen gas generated in theanode 11 is discharged to the anode solution flow path 12 together withthe anode solution. This makes it possible to prevent the oxygen gasfrom staying between the anode 11 and the separator 30, and it becomespossible to suppress a variation in a cell voltage due to the voltagevariation of the anode.

To the first flow path plate 14, there are provided a solution inletport and a solution outlet port whose illustrations are omitted, and theanode solution is introduced and discharged by the anode solution supplysystem 100 via these solution inlet port and solution outlet port. It ispreferable to use a material having low chemical reactivity and highconductivity for the first flow path plate 14. As such a material, therecan be cited a metal material such as Ti or SUS, carbon, or the like. Itis preferable that the anode solution flow path 12 is provided with aplurality of lands (convex portions) 15, as illustrated in FIG. 3. Thelands 15 are provided for mechanical retention and electricalcontinuity. The lands 15 are preferably provided in an alternate mannerfor uniformizing the flow of the anode solution. Since the lands 15 asabove are provided, the anode solution flow path 12 meanders. Inaddition, also for the purpose of realizing good discharge of the anodesolution containing oxygen (O₂) gas mixed therein, it is preferable thatthe lands 15 are provided in an alternate manner to the anode solutionflow path 12 to make the anode solution flow path 12 meander.

It is preferable that the anode 11 is mainly constituted of a catalystmaterial (anode catalyst material) capable of oxidizing water (H₂O) toproduce oxygen or hydrogen ions or oxidizing hydroxide ions (OH⁻) toproduce water or oxygen, and capable of reducing an overvoltage in sucha reaction. As such a catalyst material, there can be cited a metal suchas platinum (Pt), palladium (Pd), or nickel (Ni), an alloy or anintermetallic compound containing the above metals, a binary metal oxidesuch as a manganese oxide (Mn—O), an iridium oxide (Ir—O), a nickeloxide (Ni—O), a cobalt oxide (Co—O), an iron oxide (Fe—O), a tin oxide(Sn—O), an indium oxide (In—O), a ruthenium oxide (Ru—O), a lithiumoxide (Li—O), or a lanthanum oxide (La—O), a ternary metal oxide such asNi—Co—O, Ni—Fe—O, La—Co—O, Ni—La—O, or Sr—Fe—O, a quaternary metal oxidesuch as Pb—Ru—Ir—O or La—Sr—Co—O, or a metal complex such as a Rucomplex or an Fe complex.

The anode 11 includes a base material having a structure capable ofmaking the anode solution or ions move between the separator 30 and theanode solution flow path 12, for example, a porous structure such as amesh material, a punching material, a porous body, or a metal fibersintered body. The base material may be constituted of a metal such astitanium (Ti), nickel (Ni), or iron (Fe), or a metal material such as analloy (for example, SUS) containing at least one of these metals, or maybe constituted of the above-described anode catalyst material. When anoxide is used as the anode catalyst material, it is preferable to form acatalyst layer in a manner that the anode catalyst material is adheredto or stacked on a surface of the base material made of theabove-described metal material. The anode catalyst material preferablyhas nanoparticles, a nanostructure, a nanowire, or the like for thepurpose of increasing the oxidation reaction. The nanostructure is astructure in which nanoscale irregularities are formed on a surface ofthe catalyst material.

The cathode 22 is an electrode (reduction electrode) which causes areduction reaction of carbon dioxide (CO₂) or a reduction reaction of acarbon compound produced thereby to produce a carbon compound such ascarbon monoxide (CO), methane (CH₄), ethane (C₂H₆), ethylene (C₂H₄),methanol (CH₃OH), ethanol (C₂H₅OH), or ethylene glycol (C₂H₆O₂). In thecathode 22, there is a case where a side reaction in which hydrogen (H₂)is produced by a reduction reaction of water (H₂O) is causedsimultaneously with the reduction reaction of carbon dioxide (CO₂). Thecathode 22 has a first surface 22 a facing the cathode solution flowpath 21, and a second surface 22 b facing the CO₂ gas flow path 23. Thecathode solution flow path 21 is disposed between the cathode 22 and theseparator 30 so that the cathode solution as an electrolytic solution isbrought into contact with the cathode 22 and the separator 30.

The cathode solution flow path 21 is formed of an opening portionprovided in a second flow path plate 25. To the second flow path plate25, there are provided a solution inlet port and a solution outlet portwhose illustrations are omitted, and the cathode solution is introducedand discharged by the cathode solution supply system 200 via thesesolution inlet port and solution outlet port. The cathode solution flowsthrough inside the cathode solution flow path 21 so as to be broughtinto contact with the cathode 22 and the separator 30. It is preferableto use a material having low chemical reactivity and having noconductivity for the second flow path plate 25 forming the cathodesolution flow path 21. As such a material, there can be cited aninsulating resin material such as an acrylic resin, polyetheretherketone(PEEK), or a fluorocarbon resin.

In the cathode 22, the reduction reaction of CO₂ occurs mainly in aportion which is brought into contact with the cathode solution. Forthis reason, it is preferable to apply an opening portion with a wideopening area to the cathode solution flow path 21, as illustrated inFIG. 4. However, in order to increase the mechanical retention and theelectrical connectivity, it is also possible to provide a land (convexportion) 26 to the cathode solution flow path 21, as illustrated in FIG.5. The land 26 of the cathode solution flow path 21 is provided at acenter portion of the cathode solution flow path 21, and is retained tothe second flow path plate 25 by a bridge portion 27 which is thinnerthan the land 26, in order not to prevent the flow of the cathodesolution in the cathode solution flow path 21. When the land 26 isprovided to the cathode solution flow path 21, the number of lands 26 ispreferably small in order to reduce a cell resistance.

The CO₂ gas flow path 23 is formed of a pit (groove portion/concaveportion) provided in a third flow path plate 28. It is preferable to usea material having low chemical reactivity and high conductivity for thethird flow path plate 28 forming the CO₂ gas flow path. As such amaterial, there can be cited a metal material such as Ti or SUS, carbon,or the like. Note that in each of the first flow path plate 14, thesecond flow path plate 25, and the third flow path plate 28, an inletport and an outlet port for a solution or gas, screw holes fortightening, and the like, whose illustrations are omitted, are provided.Further, in front of and behind each of the flow path plates 14, 25, and28, packing whose illustration is omitted is sandwiched according toneed.

To the third flow path plate 28, a gas inlet port and a gas outlet portwhose illustrations are omitted are provided, and CO₂ gas or gascontaining CO₂ (sometimes collectively referred to simply as CO₂ gas) isintroduced and discharged by the gas supply system 300 via these gasinlet port and gas outlet port. The CO₂ gas flows through inside the CO₂gas flow path 23 so as to be brought into contact with the cathode 22.It is preferable that the CO₂ gas flow path 23 is provided with aplurality of lands (convex portions) 29, as illustrated in FIG. 6. Thelands 29 are provided for mechanical retention and electricalcontinuity. The lands 29 are preferably provided in an alternate manner,which realizes a state where the CO₂ gas flow path 23 meanders similarlyto the anode solution flow path 12. The cathode current collector 24 iselectrically brought into contact with a surface on a side opposite tothe cathode 22 of the third flow path plate 28.

In the electrolysis cell 2 of the embodiment, by providing the lands 15and 29 to the anode solution flow path 12 and the CO₂ gas flow path 23,it is possible to increase a contact area between the anode 11 and thefirst flow path plate 14 forming the anode solution flow path 12, and acontact area between the cathode 22 and the third flow path plate 28forming the CO₂ gas flow path 23. Further, by providing the land 26 tothe cathode solution flow path 21, it is possible to increase a contactarea between the cathode 22 and the second flow path plate 25 formingthe cathode solution flow path 21. These realize good electricalcontinuity between the anode current collector 13 and the cathodecurrent collector 24 while enhancing mechanical retentivity of theelectrolysis cell 2, and it becomes possible to improve reductionreaction efficiency of CO₂, and the like.

As illustrated in FIG. 7, the cathode 22 has a gas diffusion layer 22Aand a cathode catalyst layer 22B provided on the gas diffusion layer22A. As illustrated in FIG. 8, it is also possible that a porous layer22C denser than the gas diffusion layer 22A is disposed between the gasdiffusion layer 22A and the cathode catalyst layer 22B. As illustratedin FIG. 9, the gas diffusion layer 22A is disposed on the CO₂ gas flowpath 23 side, and the cathode catalyst layer 22B is disposed on thecathode solution flow path 21 side. The cathode catalyst layer 22B mayenter the gas diffusion layer 22A. The cathode catalyst layer 22Bpreferably has catalyst nanoparticles, a catalyst nanostructure, or thelike. The gas diffusion layer 22A is constituted of, for example, carbonpaper, carbon cloth, or the like, and water repellent treatment isperformed thereon. The porous layer 22C is constituted of a porous bodywhose pore size is smaller than that of the carbon paper or the carboncloth.

As illustrated in a schematic view in FIG. 9, in the cathode catalystlayer 22B, the cathode solution or ions are supplied and discharged fromthe cathode solution flow path 21. In the gas diffusion layer 22A, theCO₂ gas is supplied from the CO₂ gas flow path 23, and a productobtained by the reduction reaction of the CO₂ gas is discharged. Bypreviously performing moderate water repellent treatment on the gasdiffusion layer 22A, the CO₂ gas reaches the cathode catalyst layer 22Bmainly through gas diffusion. The reduction reaction of CO₂ or thereduction reaction of a carbon compound produced thereby occurs in thevicinity of a boundary between the gas diffusion layer 22A and thecathode catalyst layer 22B or in the vicinity of the cathode catalystlayer 22B which enters the gas diffusion layer 22A, a gaseous product isdischarged mainly from the CO₂ gas flow path 23, and a liquid product isdischarged mainly from the cathode solution flow path 21.

The cathode catalyst layer 22B is preferably constituted of a catalystmaterial (cathode catalyst material) capable of reducing carbon dioxideto produce a carbon compound, capable of reducing the carbon compoundproduced thereby to produce a carbon compound according to need, andcapable of reducing an overvoltage in the above reaction. As such amaterial, there can be cited a metal such as gold (Au), silver (Ag),copper (Cu), platinum (Pt), palladium (Pd), nickel (Ni), cobalt (Co),iron (Fe), manganese (Mn), titanium (Ti), cadmium (Cd), zinc (Zn),indium (In), gallium (Ga), lead (Pb), or tin (Sn), a metal material suchas an alloy or an intermetallic compound containing at least one of theabove metals, a carbon material such as carbon (C), graphene, CNT(carbon nanotube), fullerene, or ketjen black, or a metal complex suchas a Ru complex or a Re complex. The cathode catalyst layer 22B canemploy various shapes such as a plate shape, a mesh shape, a wire shape,a particle shape, a porous shape, a thin film shape, and an islandshape.

The cathode catalyst material constituting the cathode catalyst layer22B preferably has nanoparticles of the above-described metal material,a nanostructure of the metal material, a nanowire of the metal material,or a composite body in which the nanoparticles of the above-describedmetal material are supported by a carbon material such as carbonparticles, a carbon nanotube, or graphene. By applying catalystnanoparticles, a catalyst nanostructure, a catalyst nanowire, a catalystnano-support structure, or the like as the cathode catalyst material, itis possible to increase reaction efficiency of the reduction reaction ofcarbon dioxide in the cathode 22.

The separator 30 is constituted of an ion exchange membrane or the likecapable of making ions move between the anode 11 and the cathode 22, andcapable of separating the anode part 10 and the cathode part 20. As theion exchange membrane, it is possible to use, for example, a cationexchange membrane such as Nafion or Flemion, or an anion exchangemembrane such as Neosepta or Selemion. As will be described later, whenan alkaline solution is used as the anode solution and the cathodesolution, and it is assumed that hydroxide ions (OH⁻) move mainly, theseparator 30 is preferably constituted of the anion exchange membrane.However, other than the ion exchange membrane, it is also possible toapply a glass filter, a porous polymeric membrane, a porous insulatingmaterial, or the like to the separator 30, as long as they are amaterial capable of making ions move between the anode 11 and thecathode 22.

Each of the anode solution and the cathode solution as the electrolyticsolution is preferably a solution containing at least water (H₂O).Because carbon dioxide (CO₂) is supplied from the CO₂ gas flow path 23,the cathode solution may contain or need not contain carbon dioxide(CO₂). To the anode solution and the cathode solution, the same solutionmay be applied or different solutions may be applied. As a solutioncontaining H₂O used as the anode solution and the cathode solution, anaqueous solution containing an arbitrary electrolyte can be cited. Asthe aqueous solution containing the electrolyte, there can be cited, forexample, an aqueous solution containing at least one selected from ahydroxide ion (OH⁻), a hydrogen ion (H⁺), a potassium ion (K⁺), a sodiumion (Na⁺), a lithium ion (Li⁺), a chloride ion (Cl⁻), a bromide ion(Br⁻), an iodide ion (I⁻), a nitrate ion (NO₃ ⁻), a sulfate ion (SO₄²⁻), a phosphate ion (PO₄ ²⁻), a borate ion (BO₃ ³⁻), and a hydrogencarbonate ion (HCO₃ ⁻). In order to reduce an electrical resistance ofthe electrolytic solution, it is preferable to use, as the anodesolution and the cathode solution, an alkaline solution in which anelectrolyte such as a potassium hydroxide or a sodium hydroxide isdissolved in high concentration.

For the cathode solution, it is also possible to use an ionic liquidwhich is made of salts of cations such as imidazolium ions or pyridiniumions and anions such as BF₄ ⁻ or PF₆ ⁻ and which is in a liquid state ina wide temperature range, or its aqueous solution. As another cathodesolution, there can be cited an amine solution of ethanolamine,imidazole, pyridine, or the like, or an aqueous solution thereof. Asamine, any of primary amine, secondary amine, and tertiary amine isapplicable.

To the anode solution flow path 12 of the anode part 10, the anodesolution is supplied from the anode solution supply system 100. Theanode solution supply system 100 circulates the anode solution so thatthe anode solution flows through inside the anode solution flow path 12.The anode solution supply system 100 has a pressure controller 101, ananode solution tank 102, a flow rate controller (pump) 103, a referenceelectrode 104, and a pressure gauge 105, and is configured to make theanode solution circulate in the anode solution flow path 12. The anodesolution tank 102 is connected to a not-illustrated gas componentcollection unit which collects a gas component such as oxygen (O₂)contained in the circulating anode solution. The anode solution isintroduced into the anode solution flow path 12 after a flow rate and apressure thereof are controlled in the pressure controller 101 and theflow rate controller 103.

To the cathode solution flow path 21 of the cathode part 20, the cathodesolution is supplied from the cathode solution supply system 200. Thecathode solution supply system 200 circulates the cathode solution sothat the cathode solution flows through inside the cathode solution flowpath 21. The cathode solution supply system 200 has a pressurecontroller 201, a cathode solution tank 202, a flow rate controller(pump) 203, a reference electrode 204, and a pressure gauge 205, and isconfigured to make the cathode solution circulate in the cathodesolution flow path 21. The cathode solution tank 202 is connected to agas component collection unit 206 which collects a gas component such ascarbon monoxide (CO) contained in the circulating cathode solution. Thecathode solution is introduced into the cathode solution flow path 21after a flow rate and a pressure thereof are controlled in the pressurecontroller 201 and the flow rate controller 203.

To the CO₂ gas flow path 23, the CO₂ gas is supplied from the gas supplysystem 300. The gas supply system 300 has a CO₂ gas cylinder 301, a flowrate controller 302, a pressure gauge 303, and a pressure controller304. The CO₂ gas is introduced into the CO₂ gas flow path 23 after aflow rate and a pressure thereof are controlled in the flow ratecontroller 302 and the pressure controller 304. The gas supply system300 is connected to the product collection system 400 which collects aproduct in the gas flowed through the CO₂ gas flow path 23. The productcollection system 400 has a gas/liquid separation unit 401 and a productcollection unit 402. A reduction product such as CO or H₂ contained inthe gas flowed through the CO₂ gas flow path 23 is accumulated in theproduct collection unit 402 via the gas/liquid separation unit 401.

The anode solution and the cathode solution circulate in the anodesolution flow path 12 and the cathode solution flow path 21 at a time ofan electrolytic reaction operation, as described above. At a time of arefresh operation of the electrolysis cell 2 to be described later, theanode solution and the cathode solution are discharged to the wastesolution collection system 600 so that the anode 11, the anode solutionflow path 12, the cathode 22, the cathode solution flow path 21, and thelike are exposed from the anode solution and the cathode solution. Thewaste solution collection system 600 has a waste solution collectiontank 601 connected to the anode solution flow path 12 and the cathodesolution flow path 21. Waste solutions of the anode solution and thecathode solution are collected in the waste solution collection tank 601by opening and closing not-illustrated valves. The opening and closingof the valves, or the like is controlled collectively by the controlsystem 500. The waste solution collection tank 601 also functions as acollection unit of a rinse solution supplied from the refresh materialsource 700. Further, a gaseous substance supplied from the refreshmaterial source 700 and containing a part of a liquid substance, is alsocollected by the waste solution collection tank 601 according to need.

The refresh material source 700 includes a gaseous substance supplysystem 710 and a rinse solution supply system 720. Note that the rinsesolution supply system 720 can be omitted according to circumstances.The gaseous substance supply system 710 has a gas tank 711 to be asupply source of a gaseous substance such as air, carbon dioxide,oxygen, nitrogen, or argon, and a pressure controller 712 which controlsa supply pressure of the gaseous substance. The rinse solution supplysystem 720 has a rinse solution tank 721 to be a supply source of arinse solution such as water and a flow rate controller (pump) 722 whichcontrols a supply flow rate or the like of the rinse solution. Thegaseous substance supply system 710 and the rinse solution supply system720 are connected to the anode solution flow path 12, the cathodesolution flow path 21, and the CO₂ gas flow path 23 via pipes. Thegaseous substance and the rinse solution are supplied to each of theflow paths 12, 21, and 23 by opening and closing not-illustrated valves.The opening and closing of the valves, or the like is controlledcollectively by the control system 500.

A part of the reduction product accumulated in the product collectionunit 402 is sent to a reduction performance detection unit 501 of thecontrol system 500. In the reduction performance detection unit 501, aproduction amount and a proportion of each product such as CO or H₂ inthe reduction product, are detected. The detected production amount andproportion of each product are input into a data collection andcontroller 502 of the control system 500. Further, the data collectionand controller 502 collects electrical data such as a cell voltage, acell current, a cathode potential, and an anode potential, pressures andpressure losses inside the anode solution flow path and the cathodesolution flow path as part of a cell performance of the electrolysiscell 2, and transmits the data to a refresh controller 503.

The data collection and controller 502 is electrically connected, viabi-directional signal lines whose illustration is partially omitted, tothe power controller 40, the pressure controller 101 and the flow ratecontroller 103 of the anode solution supply system 100, the pressurecontroller 201 and the flow rate controller 203 of the cathode solutionsupply system 200, the flow rate controller 302 and the pressurecontroller 304 of the gas supply system 300, and the pressure controller712 and the flow rate controller 722 of the refresh material source 700,in addition to the reduction performance detection unit 501, and theseare collectively controlled. Note that each pipe is provided with anot-illustrated valve, and an opening/closing operation of the valve iscontrolled by a signal from the data collection and controller 502. Thedata collection and controller 502 may also control operations of theaforementioned components at a time of an electrolysis operation, forexample.

The refresh controller 503 is electrically connected, via bi-directionalsignal lines whose illustration is partially omitted, to the powercontroller 40, the flow rate controller 103 of the anode solution supplysystem 100, the flow rate controller 203 of the cathode solution supplysystem 200, the flow rate controller 302 of the gas supply system 300,and the pressure controller 712 and the flow rate controller 722 of therefresh material source 700, and these are collectively controlled. Notethat each pipe is provided with a not-illustrated valve, and anopening/closing operation of the valve is controlled by a signal fromthe refresh controller 503. The refresh controller 503 may also controloperations of the aforementioned components at a time of theelectrolysis operation, for example. Further, it is also possible thatthe refresh controller 503 and the data collection and controller 502are configured by one controller.

A working operation of the carbon dioxide electrolytic device 1 of theembodiment will be described. First, as illustrated in FIG. 10, astart-up step S101 of the electrolytic device 1 is performed. In thestart-up step S101 of the electrolytic device 1, the following operationis performed. In the anode solution supply system 100, a flow rate and apressure are controlled by the pressure controller 101 and the flow ratecontroller 103, and the anode solution is introduced into the anodesolution flow path 12. In the cathode solution supply system 200, a flowrate and a pressure are controlled by the pressure controller 201 andthe flow rate controller 203, and the cathode solution is introducedinto the cathode solution flow path 21. In the gas supply system 300, aflow rate and a pressure are controlled by the flow rate controller 302and the pressure controller 304, and CO₂ gas is introduced into the CO₂gas flow path 23.

Next, a CO₂ electrolysis operation step S102 is performed. In the CO₂electrolysis operation step S102, application of an electrolytic voltageis started by the power controller 40 of the electrolytic device 1 afterbeing subjected to the start-up step S101, and a current is supplied byapplying the voltage between the anode 11 and the cathode 22. When thecurrent is made to flow between the anode 11 and the cathode 22, anoxidation reaction in the vicinity of the anode 11 and a reductionreaction in the vicinity of the cathode 22 occur, which will bedescribed below. Here, a case of producing carbon monoxide (CO) as thecarbon compound is mainly described, but, the carbon compound as thereduction product of carbon dioxide is not limited to carbon monoxide,and may be other carbon compounds such as the above-described organiccompounds. Further, as a reaction process caused by the electrolysiscell 2, there can be considered a case where hydrogen ions (H⁺) aremainly produced and a case where hydroxide ions (OH⁻) are mainlyproduced, but, it is not limited to either of these reaction processes.

First, the reaction process in a case of mainly oxidizing water (H₂O) toproduce hydrogen ions (H⁺) is described. When a current is suppliedbetween the anode 11 and the cathode 22 from the power controller 40, anoxidation reaction of water (H₂O) occurs in the anode 11 which isbrought into contact with the anode solution. Concretely, as presentedin the following formula (1), H₂O contained in the anode solution isoxidized, and oxygen (O₂) and hydrogen ions (H⁺) are produced.2H₂O→4H⁺+O₂+4e ⁻  (1)

H⁺ produced in the anode 11 moves in the anode solution existing in theanode 11, the separator 30, and the cathode solution in the cathodesolution flow path 21, and reaches the vicinity of the cathode 22. Thereduction reaction of carbon dioxide (CO₂) occurs by electrons (e⁻)based on the current supplied from the power controller 40 to thecathode 22 and H⁺ moved to the vicinity of the cathode 22. Concretely,as presented in the following formula (2), CO₂ supplied from the CO₂ gasflow path 23 to the cathode 22 is reduced, and CO is produced.2CO₂+4H⁺+4e ⁻→2CO+2H₂O  (2)

Next, the reaction process in a case of mainly reducing carbon dioxide(CO₂) to produce hydroxide ions (OH⁻) is described. When a current issupplied between the anode 11 and the cathode 22 from the powercontroller 40, in the vicinity of the cathode 22, water (H₂O) and carbondioxide (CO₂) are reduced, and carbon monoxide (CO) and hydroxide ions(OH⁻) are produced, as presented in the following formula (3). Thehydroxide ions (OH⁻) diffuse to the vicinity of the anode 11, and aspresented in the following formula (4), the hydroxide ions (OH⁻) areoxidized, and oxygen (O₂) is produced.2CO₂+2H₂O+4e ⁻→2CO+4OH⁻  (3)4OH⁻→2H₂O+O₂+4e ⁻  (4)

In the above-described reaction processes in the cathode 22, thereduction reaction of CO₂ is considered to occur in the vicinity of theboundary between the gas diffusion layer 22A and the cathode catalystlayer 22B, as described above. At this time, the cathode solution whichflows through the cathode solution flow path 21 enters up to the gasdiffusion layer 22A or the cathode catalyst layer 22B has excess water,which causes a trouble such that the production amount of CO obtained bythe reduction reaction of CO₂ reduces or the cell voltage increases. Thereduction in the cell performance of the electrolysis cell 2 as above isalso caused by not only deviation of distribution of ions and residualgas in the vicinity of the anode 11 and the cathode 22, the excess waterin the cathode catalyst layer 22B, and precipitation of an electrolytein the cathode 22 and the anode 11, but also precipitation of anelectrolyte in the anode solution flow path 12 and the cathode solutionflow path 21, and the like.

Further, there is a case where the electrolysis operation causesprecipitation of salts in the cathode solution flow path 21 or the gasdiffusion layer 22A, which blocks the flow path or reduces the gasdiffusibility, resulting in that the cell performance reduces. This isbecause ions move between the anode 11 and the cathode 22 via theseparator 30 or the ion exchange membrane, and the ions react with thegas component. For example, when a potassium hydroxide solution is usedas the anode solution, and carbon dioxide gas is used as the cathodegas, potassium ions move from the anode 11 to the cathode 22, and theions react with carbon dioxide to produce salts of potassium hydroxide,potassium carbonate, or the like. In the cathode solution flow path 21or the gas diffusion layer 22A, when an amount of the salts is equal toor less than the solubility, the salts precipitate in the cathodesolution flow path 21 or the gas diffusion layer 22A. When the flow pathis blocked, a uniform gas flow in the entire cell is prevented, and thecell performance lowers. In particular, when a plurality of cathodesolution flow paths 21 are provided, the cell performance significantlylowers. Note that there is a case where the performance of the cellitself is improved by partial increase in the gas flow rate and thelike. This is because since a gas pressure is increased, the gascomponent or the like supplied to the catalyst increases or the gasdiffusibility increases, which improves the cell performance. In orderto detect the reduction in the cell performance as above, a step S103which determines whether or not the cell performance satisfies therequest criteria, is performed.

The data collection and controller 502 collects the production amountand the proportion of each product and the cell performance such as thecell voltage, the cell current, the cathode potential, the anodepotential, the pressure inside the anode solution flow path 12, thepressure inside the cathode solution flow path 21 in the electrolysiscell 2 regularly or continuously, for example, as described above.Further, in the data collection and controller 502, the request criteriaof the cell performance are previously set, and it is determined whetheror not collected data satisfies the set request criteria. When thecollected data satisfies the set request criteria, the CO₂ electrolysisoperation S102 is continued without performing a CO₂ electrolysis stop(S104). When the collected data does not satisfy the set requestcriteria, a refresh operation step S105 is performed.

The cell performance collected by the data collection and controller 502is defined by parameters such as an upper limit value of a cell voltagewhen a constant current is made to flow through the electrolysis cell 2,a lower limit value of a cell current when a constant voltage is appliedto the electrolysis cell 2, and Faradaic efficiency of the carboncompound produced by the reduction reaction of CO₂. Here, the Faradaicefficiency is defined as a proportion of a current contributing toproduction of an intended carbon compound with respect to an entirecurrent flowed through the electrolysis cell 2. In order to maintainelectrolysis efficiency, the refresh operation step S105 may beperformed when the upper limit value of the cell voltage when theconstant current is made to flow reaches 150% or more, preferably 120%or more of a set value. Further, the refresh operation step S105 may beperformed when the lower limit value of the cell current at a time ofapplying the constant voltage reaches 50% or less, preferably 80% orless of a set value. In order to maintain a production amount of thereduction product such as the carbon compound, the refresh operationstep S105 may be performed when the Faradaic efficiency of the carboncompound becomes 50% or less, preferably 80% or less of a set value.

Regarding the determination of the cell performance, for example, whenat least one parameter of the cell voltage, the cell current, theFaradaic efficiency of the carbon compound, the pressure inside theanode solution flow path 12, and the pressure inside the cathodesolution flow path 21 does not satisfy the request criteria, it isdetermined that the cell performance does not satisfy the requestcriteria, and the refresh operation step S105 is carried out. Further,it is also possible to set the request criteria of the cell performanceby combining two or more of the aforementioned parameters. For example,it is also possible to perform the refresh operation step S105 whenneither the cell voltage nor the Faradaic efficiency of the carboncompound satisfies the request criteria. The refresh operation step S105is performed when at least one of the cell performance does not satisfythe request criteria. In order to stably perform the CO₂ electrolysisoperation step S102, the refresh operation step S105 is preferablyperformed at an interval of one hour or more, for example.

If the request criteria of the cell performance are judged based on onlyone of the cell voltage, the cell current, and the Faradaic efficiencyof the carbon compound, when, even in a case where the cell performanceimproves or does not change, salts precipitate in the flow path or thegas diffusion layer to reduce the output, it is sometimes judged thatthe refresh is not required. In the electrolytic device, it is importantto suspect the reduction in the cell performance beforehand, and toperform the refresh operation at an optimum timing. Accordingly, in theelectrolytic device of the embodiment, it is preferable that thepressure in the cell (the pressure inside the anode solution flow path12, the pressure inside the cathode solution flow path 21, or the like)is set to one of the parameters for defining the request criteria, tothereby sense the precipitation of salts, and the refresh operation isperformed.

The judgment regarding the necessity of the refresh operation is madebased on not only the cell voltage, the current value, and the sensingof salts based on a voltage change in the cell, but also the performanceof gas/liquid separation between the anode 11 and the cathode 22 whenthe anode 11 and the cathode 22 are separated by the separator 30,namely, a movement amount of the liquid or the gas between the anode 11and the cathode 22, an amount of the product, a voltage differencerelative to a reference electrode, an estimated value of the Faradaicefficiency from these parameters, and the like. The Faradaic efficiencyfrom the respective parameter values and the necessity of the refreshoperation can be comprehensively determined as judgment of the necessityof the refresh operation also from parameters to be described later, andany combination of respective values and any calculation method areapplicable.

It is also possible to judge the necessity of the refresh operationbased on a flooding degree estimated from respective pieces of celldata, a voltage change, and the like based on an operating method fordetecting a flooding performance. Further, it is also possible to takean operating time of the electrolysis cell 2 into consideration. Theoperating time is not limited to an operating time after the operationis started, but may be an integrated value of the operating time so far,a duration, an operating time after the refresh operation, a calculatedvalue of multiplication between the integrated voltage value and time,or between the current value and the time, or the like, and anycombination and calculation method thereof can be applied. Further, thecalculated values of these combinations are preferable when compared tothe judgment based on simply the duration or the like, since adifference caused by the operating method of the electrolysis cell 2 istaken into consideration. Furthermore, it is also possible to use avariation value of the current or the voltage, a pH value and a changevalue of the electrolytic solution, oxygen generation amount andvariation amount.

It is preferable that the operation of judging the necessity of therefresh operation is performed, and the judgment is made based on theparameter such as a cell voltage at a time of the operation, since it ispossible to accurately judge the necessity of the refresh operation,although the working operation time is reduced. Note that a judgmenttime of the necessity of the refresh operation in this case ispreferably at least half a refresh operation time, more preferably ¼ orless of the refresh operation time, and ideally 1/10 or less of therefresh operation time. Further, regarding the respective parameters forjudging the necessity of the refresh operation, respective pieces ofdata of the electrolysis cell 2 are collected via an electronic network,required parameters are derived by the data collection and controllers502 and analysis units 504 of a plurality of cells, through big dataanalysis, and analysis of machine learning or the like, the refreshcontroller 503 is made to update the request criteria of the cellperformance defined by the respective parameters for judging thenecessity of refresh, and in a manner as above, it is possible toconstantly perform the best refresh operation.

The refresh operation step S105 is performed according to a flow chartillustrated in FIG. 11, for example. First, the application of theelectrolytic voltage performed by the power controller 40 is stopped, tothereby stop the reduction reaction of CO₂ (S201). At this time, theapplication of the electrolytic voltage does not necessarily have to bestopped. Next, the cathode solution and the anode solution aredischarged from the cathode solution flow path 21 and the anode solutionflow path 12 (S202). Next, the rinse solution is supplied to the cathodesolution flow path 21 and the anode solution flow path 12 (S203), tothereby perform washing. While the rinse solution is supplied, a refreshvoltage is applied between the anode 11 and the cathode 22. This makesit possible to remove ions and impurities adhered to the cathodecatalyst layer 22B. When the refresh voltage is applied so as to performmainly oxidation treatment, ions and impurities such as organic mattersadhered to the surface of the catalyst are oxidized to be removed.Further, by performing this treatment in the rinse solution, it ispossible to perform not only the refresh of the catalyst but alsoremoval of ions substituted in an ion-exchange resin at a time of usingthe ion exchange membrane as the separator 30.

The refresh voltage is preferably not less than −2.5 V nor more than 2.5V, for example. Since energy is used for the refresh operation, therange of the refresh voltage is preferably as narrow as possible, andthe range is more preferably not less than −1.5 V nor more than 1.5 V,for example. The refresh voltage may be cyclically applied so that theoxidation treatment of the ions and the impurities and the reductiontreatment are alternately performed. This makes it possible toaccelerate regeneration of the ion-exchange resin and regeneration ofthe catalyst. Further, it is also possible to perform the refreshoperation by applying, as the refresh voltage, a voltage whose value isequal to that of the electrolytic voltage at a time of the electrolysisoperation. In this case, it is possible to simplify the configuration ofthe power controller 40.

Next, gas is supplied to the cathode solution flow path 21 and the anodesolution flow path 12 (S204), to thereby dry the cathode 22 and theanode 11. When the rinse solution is supplied to the cathode solutionflow path 21 and the anode solution flow path 12, a saturation degree ofwater in the gas diffusion layer 22A increases, and output reductionoccurs due to the diffusibility of gas. By supplying the gas, thesaturation degree of water lowers, so that the cell performance isrecovered, and the refresh effect is increased. The gas is preferablysupplied right after the rinse solution is made to flow, and ispreferably supplied at least within five minutes after the finish ofsupply of the rinse solution. This is because the output reduction islarge due to the increase in the saturation degree of water, and if itis assumed that the refresh operation is performed at intervals of anhour, for example, an output during the refresh operation in fiveminutes is 0 V or significantly small, so that 5/60 of the output issometimes lost.

When the above refresh operation finishes, the cathode solution isintroduced into the cathode solution flow path 21, the anode solution isintroduced into the anode solution flow path 12, and CO₂ gas isintroduced into the CO₂ gas flow path 23 (S205). Subsequently, theapplication of the electrolytic voltage between the anode 11 and thecathode 22 performed by the power controller 40 is resumed, to therebyresume the CO₂ electrolysis operation (S206). Note that when theapplication of the electrolytic voltage is not stopped in S201, theaforementioned resume operation is not performed. For the discharge ofthe cathode solution and the anode solution from each of the flow paths12 and 21, gas may be used or the rinse solution may be used.

The supply and flow of the rinse solution (S203) are performed for thepurpose of preventing precipitation of an electrolyte contained in thecathode solution and the anode solution, and washing the cathode 22, theanode 11, and each of the flow paths 12 and 21. For this reason, as therinse solution, water is preferable, water having an electricconductivity of 1 mS/m or less is more preferable, and water having theelectric conductivity of 0.1 mS/m or less is still more preferable. Inorder to remove a precipitate such as the electrolyte in the cathode 22,the anode 11, and the like, an acid rinse solution having a lowconcentration, of sulfuric acid, nitric acid, hydrochloric acid, or thelike may be supplied, and the electrolyte may be dissolved by using theacid rinse solution. When the acid rinse solution having a lowconcentration is used, a step in which the rinse solution of water issupplied is performed in a step thereafter. It is preferable to perform,right before the gas supply step, the supply step of the rinse solutionof water, in order to prevent an additive contained in the rinsesolution from remaining. FIG. 1 illustrates the rinse solution supplysystem 720 having one rinse solution tank 721, but, when a plurality ofrinse solutions such as water and the acid rinse solution are used, aplurality of rinse solution tanks 721 corresponding thereto are used.

In particular, for the refresh of the ion-exchange resin, acid oralkaline rinse solution is preferable. This provides an effect ofdischarging cations or anions substituted in place of protons or OH⁻ inthe ion-exchange resin. For this reason, it is preferable that the acidrinse solution and the alkaline rinse solution are made to flowalternately, the rinse solution is combined with water having anelectric conductivity of 1 mS/m or less, and gas is supplied betweensupplies of a plurality of rinse solutions so that the rinse solutionsare not mixed.

As the rinse solution, water produced through a reaction may also beused. For example, when CO is produced from CO₂ and protons throughreduction, water is generated. It is possible that the water dischargedfrom the cathode 22 at this time is separated through gas/liquidseparation, and stored to be used. If it is designed as above, there isno need to newly supply the rinse solution from the outside, which isadvantageous in terms of system. Further, by changing an electricpotential to increase a reaction current, and increasing an amount ofwater to be produced, the water may also be supplied to the cathodesolution flow path 21. Accordingly, the tank for the produced water, andthe pipe, the pump, and the like used for the rinse solution becomeunnecessary, which provides a configuration that is effective in termsof system. Further, it is also possible that gas containing oxygen issupplied to the cathode solution flow path 21 and a voltage is applied,to thereby perform water decomposition on the electrolytic solution orthe rinse solution of the anode 11, and the refresh operation isperformed by using water produced by the catalyst from protons or OH⁻ions moved to a counter electrode. For example, in a case where Nafionis used as an ion exchange membrane in an electrolysis cell in which CO₂is reduced to CO by using a gold catalyst, when air is flowed throughthe cathode 22 and an electric potential is applied to the cell toperform water decomposition, protons moved to the cathode 22 are reactedwith oxygen by the catalyst, and water is produced. The refreshoperation can be performed by using the produced water. Further, it isalso possible that hydrogen gas is generated by supplying gas containingno oxygen to the cathode 22 or stopping the supply of gas thereafter,and the generated hydrogen is used to perform the refresh operation todry the cathode 22. Accordingly, it is also possible to perform therefresh operation of the catalyst by using reducing power of protons andhydrogen.

The gas used for the gas supply and the flow step S204 preferablycontains at least one of air, carbon dioxide, oxygen, nitrogen, andargon. Moreover, gas having low chemical reactivity is preferably used.Form such a point, air, nitrogen, and argon are preferably used, andnitrogen and argon are more preferable. The supply of the rinse solutionand gas for refresh is not limited only to the cathode solution flowpath 21 and the anode solution flow path 12, and in order to wash asurface, of the cathode 22, which is brought into contact with the CO₂gas flow path 23, the rinse solution and the gas may be supplied to theCO₂ gas flow path 23. It is effective to supply the gas to the CO₂ gasflow path 23 in order to dry the cathode 22 also from the side of thesurface which is brought into contact with the CO₂ gas flow path 23.

The above is the description regarding the case where the rinse solutionand gas for refresh are supplied to both the anode part 10 and thecathode part 20, but, the rinse solution and gas for refresh may besupplied to only one of the anode part 10 and the cathode part 20. Forexample, the Faradaic efficiency of the carbon compound varies dependingon a contact region between the cathode solution and CO₂ in the gasdiffusion layer 22A and the cathode catalyst layer 22B of the cathode22. In such a case, only by supplying the rinse solution and gas forrefresh to only the cathode part 20, the Faradaic efficiency of thecarbon compound is sometimes recovered. Depending on a type of theelectrolytic solutions (anode solution and cathode solution) to be used,there is sometimes a tendency that precipitation easily occurs in one ofthe anode part 10 and the cathode part 20. Based on such a tendency ofthe electrolytic device 1, the rinse solution and gas for refresh may besupplied to only one of the anode part 10 and the cathode part 20.Moreover, depending on an operating time or the like of the electrolyticdevice 1, the cell performance is sometimes recovered only by drying theanode 11 and the cathode 22. In such a case, it is also possible tosupply only the gas for refresh to at least one of the anode part 10 andthe cathode part 20. The refresh operation step S105 can be changed invarious ways according to an operation condition, a tendency, and thelike of the electrolytic device 1.

As described above, in the electrolytic device 1 of the firstembodiment, based on whether or not the cell performance of theelectrolysis cell 2 satisfies the request criteria, it is determinedwhether the CO₂ electrolysis operation step S102 is continued or therefresh operation step S105 is performed. By supplying the rinsesolution and gas for refresh in the refresh operation step S105, theentry of the cathode solution into the gas diffusion layer 22A, theexcess water of the cathode catalyst layer 22B, the deviation of thedistribution of the ions and the residual gas in the vicinity of theanode 11 and the cathode 22, the precipitation of the electrolyte in thecathode 22, the anode 11, the anode solution flow path 12, and thecathode solution flow path 21, and the like, which become causes ofreducing the cell performance, are removed. Therefore, by resuming theCO₂ electrolysis operation step S102 after the refresh operation stepS105, the cell performance of the electrolysis cell 2 can be recovered.By repeating the CO₂ electrolysis operation step S102 and the refreshoperation step S105 as above based on the request criteria of the cellperformance, it becomes possible to maintain the CO₂ electrolysisperformance obtained by the electrolytic device 1 for a long period oftime.

Second Embodiment

FIG. 12 is a view illustrating a configuration of a carbon dioxideelectrolytic device according to a second embodiment, and FIG. 13 is asectional view illustrating a configuration of an electrolysis cell inthe electrolytic device illustrated in FIG. 12. A carbon dioxideelectrolytic device 1X illustrated in FIG. 12 includes an electrolysiscell 2X, an anode solution supply system 100 which supplies an anodesolution to the electrolysis cell 2X, a cathode solution supply system200 which supplies a cathode solution to the electrolysis cell 2X, a gassupply system 300 which supplies carbon dioxide (CO₂) gas to theelectrolysis cell 2X, a product collection system 400 which collects aproduct produced by a reduction reaction in the electrolysis cell 2X, acontrol system 500 which detects a type and a production amount of thecollected product, and performs control of the product and control of arefresh operation, a waste solution collection system 600 which collectsa waste solution of the cathode solution and the anode solution, and arefresh material source 700 which recovers an anode, a cathode, or thelike of the electrolysis cell 2X, similarly to the carbon dioxideelectrolytic device 1 according to the first embodiment.

The carbon dioxide electrolytic device 1X illustrated in FIG. 12basically includes a configuration similar to that of the electrolyticdevice 1 illustrated in FIG. 1, except that a configuration of theelectrolysis cell 2X is different. As illustrated in FIG. 13, theelectrolysis cell 2X includes a reaction tank 53 having an anodesolution tank 51, a cathode solution tank 52, and a separator 30 whichseparates these anode solution tank 51 and cathode solution tank 52. Theanode solution tank 51 has a solution inlet port 54A and a solutiondischarge port 55A connected to the anode solution supply system 100,and a gas inlet port 56A and a gas discharge port 57A. An anode solutionis introduced from and discharged to the anode solution supply system100 to/from the anode solution tank 51. An anode 11 is disposed in theanode solution tank 51 so as to be immersed into the anode solution. Theanode 11 is connected to a power controller 40 via a currentintroduction portion 58A.

The cathode solution tank 52 has a solution inlet port 54B and asolution discharge port 55B connected to the cathode solution supplysystem 200, and a gas inlet port 56B and a gas discharge port 57Bconnected to the gas supply system 300. A cathode solution is introducedfrom and discharged to the cathode solution supply system 200 to/fromthe cathode solution tank 52. Moreover, CO₂ gas is introduced from thegas supply system 300 into the cathode solution tank 52, and gascontaining a gaseous product is sent to the product collection system400. In order to increase solubility of the CO₂ gas in the cathodesolution, the CO₂ gas is preferably released into the cathode solutionfrom the gas inlet port 56B. A cathode 22 is disposed in the cathodesolution tank 52 so as to be immersed into the cathode solution. Thecathode 22 is connected to the power controller 40 via a currentintroduction portion 58B.

A gaseous substance supply system 710 of the refresh material source 700is connected to the gas inlet port 56A of the anode solution tank 51 andthe gas inlet port 56B of the cathode solution tank 52 via pipes. Arinse solution supply system 720 of the refresh material source 700 isconnected to the solution inlet port 54A of the anode solution tank 51and the solution inlet port 54B of the cathode solution tank 52 viapipes. The solution discharge port 55A of the anode solution tank 51 andthe solution discharge port 55B of the cathode solution tank 52 areconnected to the waste solution collection system 600 via pipes. The gasdischarge port 57A of the anode solution tank 51 and the gas dischargeport 57B of the cathode solution tank 52 are connected to the wastesolution collection system 600 via pipes, and gas is recovered into anot-illustrated waste gas collection tank via the waste solutioncollection system 600 or released into the atmosphere. Composingmaterials and the like of the respective parts are similar to those ofthe electrolytic device 1 of the first embodiment, and details thereofare as described above.

In the electrolytic device 1X of the second embodiment, a start-up stepS101 of the electrolytic device 1X and a CO₂ electrolysis operation stepS102 are performed in a similar manner to the electrolytic device 1 ofthe first embodiment, except that supply modes of the anode solution,the cathode solution, and the CO₂ gas are different. A determinationstep S103 regarding whether or not the request criteria of the cellperformance are satisfied, is also performed in a similar manner to theelectrolytic device 1 of the first embodiment. When it is determinedthat the cell performance does not satisfy the request criteria, arefresh operation step S105 is performed. In the electrolytic device 1Xof the second embodiment, the refresh operation step S105 is performedas follows.

First, a CO₂ reduction reaction is stopped. Next, the anode solution andthe cathode solution are discharged from the anode solution tank 51 andthe cathode solution tank 52. At this time, application of anelectrolytic voltage performed by the power controller 40 may bemaintained or stopped. Next, a rinse solution is supplied from the rinsesolution supply system 720 to the anode solution tank 51 and the cathodesolution tank 52, to thereby wash the anode 11 and the cathode 22. Whilethe rinse solution is supplied, a refresh voltage is applied between theanode 11 and the cathode 22, in a similar manner to the firstembodiment. Next, gas is supplied from the gaseous substance supplysystem 710 to the anode solution tank 51 and the cathode solution tank52, to thereby dry the anode 11 and the cathode 22. The gas and therinse solution used for the refresh operation step S105 are similar tothose in the first embodiment. When the above refresh operationfinishes, the anode solution is introduced into the anode solution tank51, the cathode solution is introduced into the cathode solution tank52, and CO₂ gas is supplied into the cathode solution. Subsequently, theCO₂ electrolysis operation is resumed. When the application of theelectrolytic voltage performed by the power controller 40 is stopped,the application is resumed. For the discharge of the cathode solutionand the anode solution from each of the solution tanks 51 and 52, gasmay be used or the rinse solution may be used. However, amounts of thecathode solution and the anode solution are larger than those in thefirst embodiment. In order to reduce a period of time of the refreshoperation, it is preferable that the solutions are discharged by usingthe gas, and then the rinse solution is supplied.

In the electrolytic device 1X of the second embodiment, the refreshoperation may also be performed as follows. The current introductionportions 58 (58A, 58B) provided to an upper portion of the electrolysiscell 2X are detached, and the anode 11 and the cathode 22 are takenoutside to be exposed from the anode solution and the cathode solution.Next, the anode 11 and the cathode 22 are immersed into the rinsesolution to be washed. While the anode 11 and the cathode 22 areimmersed into the rinse solution, a refresh voltage is applied betweenthe anode 11 and the cathode 22, in a similar manner to the firstembodiment. Next, the anode 11 and the cathode 22 are taken out from therinse solution, and dried by blowing gas. Next, the current introductionportions 58 (58A, 58B) are attached, and the anode 11 and the cathode 22are immersed into the anode solution and the cathode solution.Subsequently, the CO₂ electrolysis operation is resumed. Accordingly,the discharge and the introduction of the anode solution and the cathodesolution from/to the anode solution tank 51 and the cathode solutiontank 52 are omitted, so that it is possible to reduce a period of timeof the refresh operation.

Also in the electrolytic device 1X of the second embodiment, based onwhether or not the cell performance of the electrolysis cell 2Xsatisfies the request criteria, it is determined whether the CO₂electrolysis operation is continued or the refresh operation isperformed. By supplying the rinse solution and the gas in the refreshoperation step, deviation of distribution of ions and residual gas inthe vicinity of the anode 11 and the cathode 22, which become a cause ofreducing the cell performance, is eliminated, and the precipitation ofthe electrolyte or the like in the anode 11 and the cathode 22 isremoved. Therefore, by resuming the CO₂ electrolysis operation after therefresh operation step, the cell performance of the electrolysis cell 2Xcan be recovered. By repeating the CO₂ electrolysis operation and therefresh operation based on the request criteria of the cell performance,it becomes possible to maintain the CO₂ electrolysis performanceobtained by the electrolytic device 1X for a long period of time.

Third Embodiment

FIG. 14 is a view illustrating a configuration of a carbon dioxideelectrolytic device according to a third embodiment, and FIG. 15 is asectional view illustrating a configuration of an electrolysis cell inthe electrolytic device illustrated in FIG. 14. A carbon dioxideelectrolytic device 1Y illustrated in FIG. 14 includes an electrolysiscell 2Y, an anode solution supply system 100 which supplies an anodesolution to the electrolysis cell 2Y, a gas supply system 300 whichsupplies carbon dioxide (CO₂) gas to the electrolysis cell 2Y, a productcollection system 400 which collects a product produced by a reductionreaction in the electrolysis cell 2Y, a control system 500 which detectsa type and a production amount of the collected product, and performscontrol of the product and control of a refresh operation, a wastesolution collection system 600 which collects a waste solution of theanode solution, and a refresh material source 700 which recovers ananode, a cathode, or the like of the electrolysis cell 2Y, similarly tothe carbon dioxide electrolytic device 1 according to the firstembodiment.

The carbon dioxide electrolytic device 1Y illustrated in FIG. 14basically includes a configuration similar to that of the electrolyticdevice 1 illustrated in FIG. 1, except that the configuration of theelectrolysis cell 2Y is different, and a cathode solution supply system200 is not included. As illustrated in FIG. 15, the electrolysis cell 2Yincludes an anode part 10, a cathode part 20, and a separator 30. Theanode part 10 includes an anode 11, an anode solution flow path 12, andan anode current collector 13. The cathode part 20 includes a cathode22, a CO₂ gas flow path 23, and a cathode current collector 24. A powercontroller 40 is connected to the anode 11 and the cathode 22 via acurrent introduction member.

The anode 11 preferably has a first surface 11 a which is brought intocontact with the separator 30, and a second surface 11 b which faces theanode solution flow path 12. The first surface 11 a of the anode 11 isbrought into close contact with the separator 30. The anode solutionflow path 12 is formed of a pit (groove portion/concave portion)provided in a flow path plate 14. The anode solution flows throughinside the anode solution flow path 12 so as to be brought into contactwith the anode 11. The anode current collector 13 is electricallybrought into contact with a surface on a side opposite to the anode 11of the flow path plate 14 which forms the anode solution flow path 12.The cathode 22 has a first surface 22 a which is brought into contactwith the separator 30, and a second surface 22 b which faces the CO₂ gasflow path 23. The CO₂ gas flow path 23 is formed of a pit (grooveportion/concave portion) provided in a flow path plate 28. The cathodecurrent collector 24 is electrically brought into contact with a surfaceon a side opposite to the cathode 22 of the flow path plate 28 whichforms the CO₂ gas flow path 23.

A gaseous substance supply system 710 and a rinse solution supply system720 of the refresh material source 700 are connected to the anodesolution flow path 12 and the CO₂ gas flow path 23 via pipes. The anodesolution flow path 12 and the CO₂ gas flow path 23 are connected to thewaste solution collection system 600 via pipes. A rinse solutiondischarged from the anode solution flow path 12 and the CO₂ gas flowpath is recovered into a waste solution collection tank 601 of the wastesolution collection system 600. Gas for refresh discharged from theanode solution flow path 12 and the CO₂ gas flow path is recovered intoa not-illustrated waste gas collection tank via the waste solutioncollection system 600 or released into the atmosphere. Composingmaterials and the like of the respective parts are similar to those ofthe electrolytic device 1 of the first embodiment, and details thereofare as described above.

In the electrolytic device 1Y of the third embodiment, a start-up stepS101 of the electrolytic device 1Y and a CO₂ electrolysis operation stepS102 are performed in a similar manner to the electrolytic device 1 ofthe first embodiment, except that supply of a cathode solution is notperformed. Note that a reduction reaction of CO₂ in the cathode part 20is performed by CO₂ supplied from the CO₂ gas flow path 23 and the anodesolution permeated the cathode 22 via the separator 30. A determinationstep S103 regarding whether or not the request criteria of the cellperformance are satisfied, is also performed in a similar manner to theelectrolytic device 1 of the first embodiment. When it is determinedthat the cell performance does not satisfy the request criteria, arefresh operation step S105 is performed. In the electrolytic device 1Yof the third embodiment, the refresh operation step S105 is performed asfollows.

First, a CO₂ reduction reaction is stopped. At this time, application ofan electrolytic voltage performed by the power controller 40 may bemaintained or stopped. Next, the anode solution is discharged from theanode solution flow path 12. Next, a rinse solution is supplied from therinse solution supply system 720 to the anode solution flow path 12 andthe CO₂ gas flow path 23, to thereby wash the anode 11 and the cathode22. While the rinse solution is supplied, a refresh voltage is appliedbetween the anode 11 and the cathode 22, in a similar manner to thefirst embodiment. Next, gas is supplied from the gaseous substancesupply system 710 to the anode solution flow path 12 and the CO₂ gasflow path 23, to thereby dry the anode 11 and the cathode 22. The gasand the rinse solution used for the refresh operation step are similarto those in the first embodiment. When the above refresh operationfinishes, the anode solution is introduced into the anode solution flowpath 12, and CO₂ gas is introduced into the CO₂ gas flow path 23.Subsequently, the CO₂ electrolysis operation is resumed. When theapplication of the electrolytic voltage performed by the powercontroller 40 is stopped, the application is resumed.

Also in the electrolytic device 1Y of the third embodiment, based onwhether or not the cell performance of the electrolysis cell 2Ysatisfies the request criteria, it is determined whether the CO₂electrolysis operation is continued or the refresh operation isperformed. By supplying the rinse solution and the gas in the refreshoperation step, deviation of distribution of ions in the vicinity of theanode 11 and the cathode 22, which become a cause of reducing the cellperformance, is eliminated, and further, excess water in the cathode 22,the precipitation of the electrolyte in the anode 11 and the cathode 22,blocking of the flow path caused by the precipitation of theelectrolyte, and the like are removed. Therefore, by resuming the CO₂electrolysis operation after the refresh operation step, the cellperformance of the electrolysis cell 2Y can be recovered. By repeatingthe CO₂ electrolysis operation and the refresh operation as above basedon the request criteria of the cell performance, it becomes possible tomaintain the CO₂ electrolysis performance obtained by the electrolyticdevice 1Y for a long period of time.

When liquid passes through the separator 30 at a relatively lowpressure, for example, a hydrophilic polytetrafluoroethylene (PTFE)porous body or the like is used, the rinse solution is supplied to onlythe anode solution flow path 12, and a pressure is applied to the liquidat an anode outlet by using a not-illustrated valve or the like or theanode outlet is blocked. Accordingly, the rinse solution passes throughthe separator 30, flows into the cathode 22, and the rinse solutionflows out from a discharge port of the cathode 22. This makes itpossible to perform the refresh of the cathode 22 and the refresh of theanode 11 at the same time. This configuration eliminates the necessityof the device which makes the rinse solution flow through the cathode22, so that the device becomes compact in size, and further, the systemis simplified, which is preferable.

Note that a pipe through which air gas is introduced into the cathode 22may be connected to the cathode 22. At a time of the refresh, it ispossible that gas containing air is supplied to the cathode 22, and arefresh voltage is applied between the anode 11 and the cathode 22, tothereby cause a water electrolysis reaction. On the anode 11 side,oxygen is generated by an oxidation catalyst, and generated protons moveto the cathode 22 through the separator 30 or an electrolyte membrane.In the cathode 22, the protons and oxygen in the air are reacted by acathode catalyst, resulting in that water is produced. By using theproduced water, salts in the cathode can be dissolved to be discharged.Further, the produced water is pure water, so that it can be used towash the cathode 22. At this time, impurities in the cathode 22 can besubjected to reduction treatment by using the protons moved to thecathode 22, and it is possible to regenerate the catalyst and themembers. This configuration eliminates the necessity of the device whichsupplies the rinse solution to the cathode 22, so that the devicebecomes compact in size, and further, the system is simplified, which ispreferable. Further, when, before the flow of the CO₂ gas to beperformed thereafter, the air flowed through the cathode is stopped, thegenerated protons react with each other to generate hydrogen, whichenables to push out generated water. When the oxygen-containing gas isstopped before performing push with CO₂, a regeneration function of thecatalyst and the members provided by the protons becomes more effective.This is because other catalysts which are difficult to be reduced andthe respective members of the cathode 22 are reduced, due to the absenceof oxygen. Concretely, there can be cited organic matters of impurities,metal oxides, and the like. When CO₂ is supplied thereafter to cause areaction, it is possible to further expect a refresh effect.

EXAMPLES

Next, examples, comparative examples, and evaluation results thereofwill be described.

Examples 1 to 8, Comparative Examples 1, 2

An electrolytic device illustrated in FIG. 14 was fabricated, and anelectrolysis performance of carbon dioxide was examined. First, on acarbon paper provided with a porous layer, a cathode to which carbonparticles on which gold nanoparticles were supported were applied, wasproduced by the following procedure. A coating solution in which thecarbon particles on which the gold nanoparticles were supported, purewater, a Nafion solution, and ethylene glycol were mixed was produced.An average particle diameter of the gold nanoparticles was 8.7 nm, and asupported amount thereof was 18.9 mass %. The coating solution wasfilled in an air brush, and spray-coated on the carbon paper providedwith the porous layer, by using Ar gas. After the coating, washing wasperformed by flowing pure water for 30 minutes, and thereafter, theorganic matter such as ethylene glycol was oxidized to be removedthrough immersion in a hydrogen peroxide solution. This was cut into asize of 2×2 cm to be set as the cathode. Note that a coating amount ofAu was estimated as about 0.2 mg/cm² from a mixing amount of the goldnanoparticles and the carbon particles in the coating solution. For ananode, an electrode in which IrO₂ nanoparticles to be a catalyst wereapplied to Ti mesh was used. As the anode, one in which IrO₂/Ti mesh wascut into 2×2 cm was used.

As illustrated in FIG. 2, the electrolysis cell 2 was produced in amanner that the cathode current collector 24, the CO₂ gas flow path 23(the third flow path plate 28), the cathode 22, the cathode solutionflow path 21 (the second flow path plate 25), the separator 30, theanode 11, and the anode solution flow path 12 (the anode currentcollector 13) were stacked in this order from the top, the stack wassandwiched by the not-illustrated support plates, and tightened by thebolts. For the separator 30, a PTFE porous body (product name: POREFLON,manufactured by Sumitomo Electric Industries, Ltd.) after beingsubjected to hydrophilic treatment was used. The IrO₂/Ti mesh of theanode 11 was brought into close contact with the PTFE porous body. Athickness of the cathode solution flow path 21 was set to 1 mm. Notethat an evaluation temperature was set to room temperature.

The electrolytic device 1 illustrated in FIG. 14 was fabricated usingthe above-described electrolysis cell 2, and the electrolytic device wasoperated under the following condition. CO₂ gas was supplied to the CO₂gas flow path of the electrolysis cell at 60 sccm, and an aqueouspotassium hydroxide solution (concentration 1 M KOH) was introduced intothe cathode solution flow path at a flow rate of 2 mL/min. Next, bycontrolling a voltage with the use of the power controller, a voltage of2.2 V was applied between the anode and the cathode to make a currentflow, an electrolytic reaction of CO₂ was caused, and a cell voltage atthat time was measured, and collected by the data collection andcontroller. Further, a part of gas output from the CO₂ gas flow path wascollected, and production amounts of CO gas produced by a reductionreaction of CO₂ and H₂ gas produced by a reduction reaction of waterwere analyzed by a gas chromatograph. In the data collection andcontroller, based on the gas production amounts, a partial currentdensity of CO or H₂, and Faradaic efficiency being a ratio between theentire current density and the partial current density were calculatedand collected.

After 31 minutes from the start of the operation, the refresh operationwas performed. In the refresh operation, while supplying distilled waterof about 1 cc to the cathode, the refresh operation was performed forabout one minute while maintaining the voltage between the anode and thecathode to a value at a time of the electrolysis operation in example 1,and then the CO₂ gas flow rate was increased to 200 ccm. A period oftime of increasing the gas flow rate was about 30 seconds. Table 1presents an entire current density, CO Faradaic efficiency, and H₂Faradaic efficiency which were collected every about 30 minutes.

In example 2, a reference electrode was disposed at an upstream portionof the anode solution flow path 12. For the reference electrode, Hg/HgOwas used. In the refresh operation, distilled water was supplied to thecathode in a similar manner to example 1, when the flow path was filledwith the distilled water, an electric potential of the anode wasadjusted so that an electric potential of the cathode with respect tothe reference electrode became 1.0 V, and the refresh operation wasperformed for about one minute. After the reaction, the supply of thedistilled water was stopped, and the CO₂ gas flow rate was increased to200 ccm. A period of time of increasing the gas flow rate was about 30seconds. Table 1 presents an entire current density, CO Faradaicefficiency, and H₂ Faradaic efficiency which were collected every about30 minutes.

In example 3, the refresh operation was performed under a conditionsimilar to that of example 2, except that the electric potential of theanode was adjusted so that the electric potential of the cathode withrespect to the electric potential of the reference electrode became 1.3V. Table 1 presents an entire current density, CO Faradaic efficiency,and H₂ Faradaic efficiency which were collected every about 30 minutes.

In example 4, the refresh operation was performed under a conditionsimilar to that of example 2, except that the electric potential of theanode was adjusted so that the electric potential of the cathode withrespect to the electric potential of the reference electrode became 1.6V. Table 1 presents an entire current density, CO Faradaic efficiency,and H₂ Faradaic efficiency which were collected every about 30 minutes.

In example 5, the refresh operation was performed under a conditionsimilar to that of example 2, except that the electric potential of theanode was adjusted so that the electric potential of the cathode withrespect to the electric potential of the reference electrode became 2.0V. Table 1 presents an entire current density, CO Faradaic efficiency,and H₂ Faradaic efficiency which were collected every about 30 minutes.

In example 6, the electric potential of the anode was adjusted so thatthe electric potential of the cathode with respect to the electricpotential of the reference electrode was changed from 0 V to 1.6 V at arate of 100 mV/s, and when the electric potential of the cathode reached1.6 V, the electric potential of the anode was adjusted so that theelectric potential of the cathode was changed at a rate of −100 mV/s.The sweep from 0 V to 1.6 V, and the sweep from 1.6 V to 0 V wererepeated three times. The refresh operation was performed under acondition similar to that of example 2 except the above. Table 1presents an entire current density, CO Faradaic efficiency, and H₂Faradaic efficiency which were collected every about 30 minutes.

In example 7, the refresh operation was performed under a conditionsimilar to that of example 6, except that the electric potential of thecathode with respect to the reference electrode was changed from −2.0 Vto 1.6 V. Table 1 presents an entire current density, CO Faradaicefficiency, and H₂ Faradaic efficiency which were collected every about30 minutes.

In example 8, distilled water was supplied to only the anode, and acathode outlet was blocked, to thereby make the distilled water move tothe cathode to be discharged from the cathode outlet. Further, therefresh operation was performed under a condition similar to that ofexample 1 except that the distilled water was supplied for one minuteand then the CO₂ flow rate with respect to the cathode was increased.Table 1 presents an entire current density, CO Faradaic efficiency, andH₂ Faradaic efficiency which were collected every about 30 minutes.

In comparative example 1, operation was continuously performed withoutperforming the refresh operation. In comparative example 2, the refreshoperation was performed without applying the voltage between the anodeand the cathode while supplying the distilled water to the cathode.Table 1 presents an entire current density, CO Faradaic efficiency, andH₂ Faradaic efficiency which were collected every about 30 minutes.

TABLE 1 Operating time 0 30 Right after 60 90 minutes minutes refreshminutes minutes Example 1 Current density (mA/cm²) 220 182 205 183 180Faradaic efficiency of CO [%] 93 95  96 95 94 Faradaic efficiency of H₂[%] 1.2 1.8  1.4 1.6 1.7 Example 2 Current density (mA/cm²) 220 182 203182 178 Faradaic efficiency of CO [%] 93 95  96 95 94 Faradaicefficiency of H₂ [%] 1.2 1.8  1.4 1.6 1.8 Example 3 Current density(mA/cm²) 220 182 206 184 180 Faradaic efficiency of CO [%] 93 95  96 9594 Faradaic efficiency of H₂ [%] 1.2 1.8  1.4 1.6 1.7 Example 4 Currentdensity (mA/cm²) 220 182 205 182 176 Faradaic efficiency of CO [%] 93 95 96 95 93 Faradaic efficiency of H₂ [%] 1.2 1.8  1.4 1.7 1.9 Example 5Current density (mA/cm²) 220 182 201 179 175 Faradaic efficiency of CO[%] 93 95  96 95 94 Faradaic efficiency of H₂ [%] 1.2 1.8  1.4 1.6 1.9Example 6 Current density (mA/cm²) 220 182 207 185 182 Faradaicefficiency of CO [%] 93 95  96 96 95 Faradaic efficiency of H₂ [%] 1.21.8  1.4 1.6 1.6 Example 7 Current density (mA/cm²) 220 182 210 187 184Faradaic efficiency of CO [%] 93 95  98 97 97 Faradaic efficiency of H₂[%] 1.2 1.8  1.4 1.4 1.5 Example 8 Current density (mA/cm²) 220 182 208186 185 Faradaic efficiency of CO [%] 93 95  98 96 95 Faradaicefficiency of H₂ [%] 1.2 1.8  1.4 1.4 1.5 Comp. Current density (mA/cm²)220 182 182(*) 176 172 Example 1 Faradaic efficiency of CO [%] 93 95 94(*) 93 92 Faradaic efficiency of H₂ [%] 1.2 1.8  1.8(*) 2.1 3.5 Comp.Current density (mA/cm²) 220 182 192 173 168 Example 2 Faradaicefficiency of CO [%] 93 95  96 95 94 Faradaic efficiency of H₂ [%] 1.21.8  1.4 1.9 2.1 (*)(Refresh is not performed)

As can be understood from Table 1, by performing the refresh operationby applying the voltage between the anode and the cathode whilesupplying the rinse solution to the cathode, it is possible to improveat least one of the current density, the CO Faradaic efficiency, and theH₂ Faradaic efficiency. This indicates that the cell performance can bemaintained for a longer period of time when compared to the prior art.

Note that configurations of the above-described respective embodimentsmay be each applied in combination, and further may be partiallysubstituted. Herein, while certain embodiments of the present inventionhave been described, these embodiments have been presented by way ofexample only, and are not intended to limit the scope of the inventions.Indeed, the novel embodiments described herein may be embodied in avariety of other forms; furthermore, various omissions, substitutions,and changes in the form of the embodiments described herein may be madewithout departing from the spirit of the inventions. The accompanyingclaims and their equivalents are intended to cover such forms ormodifications as would fall within the scope and spirit of theinvention.

What is claimed is:
 1. A carbon dioxide electrolytic device, comprising:an electrolysis cell including a cathode to reduce carbon dioxide andthus produce a carbon compound, an anode to oxidize water or hydroxideions and thus produce oxygen, a carbon dioxide source to supply carbondioxide to the cathode, a solution source to supply an electrolyticsolution containing water to at least one selected from the groupconsisting of the cathode and the anode, and a separator separating theanode and the cathode; a power controller connected to the anode and thecathode and configured to apply a voltage therebetween; a refreshmaterial source including a gas source to supply a gaseous substance toat least one selected from the group consisting of the anode and thecathode, and a solution supply source to supply a rinse solution to atleast one selected from the group consisting of the anode and thecathode; and a controller to control the carbon dioxide source, thesolution source, the power controller, and the refresh material sourcein accordance with request criteria of a performance of the cell andthus stop the supply of the carbon dioxide and the electrolyticsolution, and apply the voltage therebetween while supplying the rinsesolution thereto.
 2. The device according to claim 1, wherein thesolution supply source includes a first solution supply source to supplyan acid rinse solution thereto, and a second solution supply source tosupply water thereto.
 3. The device according to claim 2, wherein thecontroller is configured to control the refresh material source tosupply the rinse solution from the solution supply source and thegaseous substance from the gas source to at least one selected from thegroup consisting of the cathode and the anode exposed from theelectrolytic solution.
 4. The device according to claim 1, furthercomprising a flow rate controller to be controlled by the controller andthus adjust a flow rate of at least one selected from the groupconsisting of the rinse solution and the gaseous substance.
 5. Thedevice according to claim 1, wherein the gaseous substance contains atleast one selected from the group consisting of air, carbon dioxide,oxygen, nitrogen, and argon.
 6. The device according to claim 1,wherein: the carbon dioxide source has a gas flow path through which thecarbon dioxide flows to the cathode; and the solution source has acathode solution flow path through which a cathode solution of theelectrolytic solution flows to the cathode, and an anode solution flowpath through which an anode solution of the electrolytic solution flowsto the anode.
 7. The device according to claim 6, wherein: the anode hasa first surface in contact with the separator, and a second surfacefacing the anode solution flow path so that the anode solution flowsfrom the anode solution flow path to the anode; the cathode has a firstsurface facing the cathode solution flow path and a second surfacefacing the gas flow path; and the cathode solution flow path is disposedbetween the separator and the cathode so that the cathode solution flowsto the separator and the cathode.
 8. The device according to claim 1,wherein: the solution source has a cathode solution tank to store acathode solution of the electrolytic solution into which the cathode isimmersed, and an anode solution tank to store an anode solution of theelectrolytic solution into which the anode is immersed; and the carbondioxide source has a carbon dioxide supply system to supply the carbondioxide to the cathode solution.
 9. The device according to claim 8,wherein: the carbon dioxide source has a gas flow path through which thecarbon dioxide flows to the cathode; the solution source has an anodesolution flow path through which the anode solution of the electrolyticsolution flows to the anode; and the cathode and the anode are disposedon the separator.
 10. The device according to claim 1, wherein theperformance is defined by a parameter including at least one selectedfrom the group consisting of a cell voltage of the cell, a cell currentof the cell, and Faradaic efficiency of the carbon compound.
 11. Thedevice according to claim 6, wherein the performance is defined byparameters including at least one selected from the group consisting ofa cell voltage of the cell, a cell current of the cell, and Faradaicefficiency of the carbon compound, and an internal pressure of at leastone selected from the group consisting of the cathode solution flow pathand the anode solution flow path.
 12. The device according to claim 11,further comprising a pressure controller to be controlled by thecontroller and thus adjust the internal pressure of at least oneselected from the group consisting of the cathode and anode solutionflow paths.
 13. A method of electrolyzing carbon dioxide, comprising:preparing an electrolysis cell having a cathode and an anode; supplyingcarbon dioxide to the cathode, and supplying an electrolytic solutioncontaining water to at least one selected from the group consisting ofthe cathode and the anode; applying a first voltage between the anodeand the cathode to reduce carbon dioxide and thus produce a carboncompound by the cathode, and to oxidize water or hydroxide ions and thusproduce oxygen by the anode; and stopping the supply of the carbondioxide and the electrolytic solution, and applying the first voltage ora second voltage therebetween while supplying a rinse solution to atleast one selected from the group consisting of the cathode, inaccordance with request criteria of a performance of the cell.
 14. Themethod according to claim 13, further comprising: discharging the rinsesolution therefrom; and supplying a gaseous substance to at least oneselected from the group consisting of the cathode and the anode afterthe discharge of the rinse solution.
 15. The method according to claim13, wherein the performance is defined by a parameter including at leastone selected from the group consisting of a cell voltage of the cell, acell current of the cell, Faradaic efficiency of the carbon compound, aninternal pressure of a cathode solution flow path through which acathode solution of the electrolytic solution flows to the cathode, andan internal pressure of an anode solution flow path through which ananode solution of the electrolytic solution flows to the anode.